Coupled Analysis of Cooled Gas Turbine Blades

Abstract

The paper presents solution aspects of the heat transfer modeling and fluid flow prediction of the convective cooled gas turbine blade. The heat transfer problem within the blade material is solved using finite element method whereas the flow problem employs the finite volume method. The flow field is calculated by solving the Navier-Stokes (NS) equations. The problem can be faced in two ways which are presented in this work. The first one is the uncoupled field method which does not take into consideration the interaction between the flowing medium and the blade. This way of solution is simpler and computationally cheap but has limited accuracy. The other one is the coupled field method (conjugate heat transfer CHT), which resolves iteratively the thermal interaction between the fluid and the blade material. The coupled method is much more accurate but one has to pay for it with longer computations as well as the algorithm stability control. As the fluid flow schemes are very sensitive to boundary condition changes, a fine time stepping with relaxation as well as an adequate mesh were required. The calculations showed another very important problem occurring in the analyses carried out. This is the laminar-turbulent transition which can significantly affect the accuracy of the results. The change of the flow character influences the heat exchange intensity and consequently the temperature distribution within the blade. Nevertheless, the problem is not yet satisfactorily worked out and the criteria of the laminar-turbulent transition are very difficult to build. The problem becomes simpler if the location of the transition point is known (i.e. from experimental data). On the basis of experimental data authors solved the problem of a blade cooling for both uncoupled and coupled method and different flow characters in order to obtain numerical results best matching the real phenomena.